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Paris (AFP) – Wolves infected with a common parasite are much more likely to become the leader of their pack, according to a new study, which suggests the brain-dwelling invader encourages its host to take more risks.
The unicellular parasite, Toxoplasma gondii, only reproduces sexually in cats, but can infect all warm-blooded animals.
It is estimated that between 30 and 50 percent of people worldwide are infected with the parasite, which remains as dormant tissue cysts for life. However, people with a healthy immune system rarely have symptoms.
While some studies have reported an association between people with the parasite in their brains and increased risk-taking, other research has disputed these findings and no definitive link has been proven.
The new study, published in the journal Communications Biology on Thursday, drew on 26 years of data on gray wolves living in the United States’ Yellowstone National Park to investigate how the parasite might influence their behavior.
The Yellowstone Wolf Project researchers analyzed the blood samples of nearly 230 wolves and 62 cougars — the big cats are known spreaders of the parasite.
They found that infected wolves were more likely to penetrate deeper into the cougars’ territory than uninfected wolves.
Infected wolves were also 11 times more likely to leave their pack than wolves without the parasite, the study said, indicating a higher degree of risk-taking.
And an infected wolf is up to 46 times more likely to become pack leader, the researchers estimate, adding that the role is normally won by more aggressive animals.
Study co-author Kira Cassidy told AFP that while “being bolder isn’t necessarily a bad thing,” it “may lower the survival rates of the most daring animals because they can make decisions that put them in danger more often.”
“Wolves don’t have the survival space to take too many more risks than they already do.”
Cassidy said it was only the second study of T. gondii’s effect on a wild animal, after research last year found that infected hyena cubs showed more audacity, making them more likely to get closer to — and killed by — lions. arrived in Kenya.
Laboratory studies have also shown that rodents with the parasite lose their instinctive fear of cats, placing them in the hands of the only host where T. gondii can reproduce.
William Sullivan, a professor of pharmacology and toxicology at Indiana University School of Medicine who has studied T.gondii for more than 25 years, called the wolf paper “a rare gem.”
However, he cautioned that such an observational study could not prove causation.
“A wolf that is a natural risk taker may be more likely to venture into the cougar’s territory and contract Toxoplasma,” he said.
But “if the findings are correct, they suggest that we may be underestimating the impact of Toxoplasma on ecosystems around the world,” he added.
What about humans?
“That’s the million-dollar question,” Sullivan said, adding that “no one knows for sure and the literature is mixed.”
Ajai Vyas, a T. gondii expert at Nanyang Technological University in Singapore, cautioned against the conclusion that infection could increase risk-taking in humans.
“There is a lot about human behavior that is different from other animals,” he told AFP.
People often become infected with T. gondii by eating undercooked meat — or through their cat, especially when cleaning out their litter boxes.
In some cases, especially in people with weakened immune systems, T. gondii can lead to toxoplasmosis, a disease that can cause brain and eye damage.
© 2022 AFP